Twin-clutch type transmission unit for engine, and motorcycle incorporating the same

Abstract

A twin-clutch type transmission unit includes inner and outer shafts provided respectively with first and second disc clutches for transmission and interruption of input from a prime mover, a plurality of drive gears provided on the inner and outer shafts, and a counter shaft provided with driven gears selectively operable to mesh with the drive gears, with the first and second disc clutches of the inner and outer shafts being alternately disengaged and engaged so as to perform a gear shift. In the transmission unit, a dog-type clutch for synchronizing rotations of the inner shaft and the outer shaft is provided. At the time of vehicle starting, the inner and outer shafts are connected with each other, and the first and second disc clutches of both the inner and outer shafts are engaged. Such transmission unit contrives reductions in the size and weight of a twin-clutch type transmission unit.

What is claimed is: 
     
       1. A twin-clutch type transmission unit comprising
 a first clutch and a second clutch; 
 a first input shaft and a second input shaft provided respectively with said clutches for transmission and interruption of input from a prime mover; 
 a plurality of drive gears provided on the first and second input shafts; 
 an output shaft provided with a plurality of driven gears operable to selectively mesh with the drive gears, with the clutches of the first input shaft and the second input shaft being alternately disengaged and engaged so as to perform a gear shift; and 
 a clutch synchronization device for synchronizing rotation of the first input shaft and rotation of the second input shaft, the clutch synchronization device comprising a first drive gear being rotationally fixed on the first input shaft and a second drive gear being rotationally fixed on the second input shaft, said clutch synchronization device being operative to directly connect the first input shaft and the second input shaft; 
 wherein, at a time of vehicle starting: 
 the first input shaft and the second input shaft are directly connected to each other by said clutch synchronization device, 
 the clutches of both the first and second input shafts are simultaneously engaged, such that 
 motive force from the prime mover is transmitted by the first clutch to the first input shaft and simultaneously by the second clutch to the second input shaft, 
 the motive force transmitted to the second input shaft by the second clutch is further transmitted from the second input shaft to the first input shaft by the clutch synchronization device, 
 a sum of the motive force transmitted from the first clutch to the first input shaft and the motive force transmitted from the clutch synchronization device to the first input shaft is transmitted from the first input shaft to the output shaft, 
 and a loading of the first and second clutches is shared during the time of vehicle starting. 
 
     
     
       2. The twin-clutch type transmission unit according to  claim 1 , wherein after the vehicle starting, the first input shaft and the second input shaft are disconnected from each other at a time when rotation of the prime mover reaches a predetermined rotating speed. 
     
     
       3. The twin-clutch type transmission unit according to  claim 2 , wherein the first input shaft and the second input shaft comprise an inner-outer double shaft having an inner input shaft and an outer input shaft; and
 wherein said clutch synchronization device for synchronizing the rotation of the first input shaft and the rotation of the second input shaft is arranged between the inner input shaft and an end portion of the outer input shaft. 
 
     
     
       4. The twin-clutch type transmission unit according to  claim 3 , wherein the clutch synchronization device comprises a dog-type clutch in which at least one of the drive gears provided at the end portion of the outer input shaft and one of the drive gears provided on the inner input shaft adjacent to the gear provided at the end portion of the outer input shaft is moved in an axial direction so as to be fitted with the other. 
     
     
       5. The twin-clutch type transmission unit according to  claim 1 , wherein said clutch synchronization device comprises one of said drive gears formed on the first input shaft having a hole formed therein, and a projection formed on one of adjacent said drive gears formed on the second input shaft; and wherein said hole is operable to engage with said projection. 
     
     
       6. The twin-clutch type transmission unit according to  claim 1 , wherein said clutch synchronization device is arranged between the first input shaft and an end portion of the second input shaft. 
     
     
       7. A twin-clutch type transmission unit comprising
 a first clutch and a second clutch; 
 a first input shaft and a second input shaft provided respectively with said clutches for transmission and interruption of input from a prime mover; 
 a plurality of drive gears provided on the first and second input shafts; 
 an output shaft provided with a plurality of driven gears operable to mesh with the drive gears, with the clutches of the first input shaft and the second input shaft being alternately disengaged and engaged so as to perform a gear shift; and 
 a clutch synchronization device for synchronizing rotation of the first input shaft and rotation of the second input shaft, the clutch synchronization device being disposed between and operative to directly connect the first input shaft and the second input shaft; 
 wherein at the time of vehicle stop, the first input shaft and the second input shaft are directly connected with each other by the clutch synchronization device, and a first input gear on the first input shaft and a second input gear on the second input shaft are respectively meshed with a first output gear and a second output gear on the output shaft, wherein the meshing of the first input gear and first output gear forms a first gear speed, the meshing of the second input gear and the second output gear forms a second gear speed, and the simultaneous engagement of the first and second gear speeds effectively locks the output shaft. 
 
     
     
       8. The twin-clutch type transmission unit according to  claim 7 , wherein after vehicle starting, the first input shaft and the second input shaft are disconnected from each other at a time when rotation of the prime mover reaches a predetermined rotating speed. 
     
     
       9. The twin-clutch type transmission unit according to  claim 7 , wherein each of the first input shaft and the second input shaft comprise an inner-outer double shaft having an inner input shaft and an outer input shaft, and the clutch synchronization device for synchronizing the rotation of the first input shaft and the rotation of the second input shaft is provided between the inner input shaft and an end portion of the outer input shaft. 
     
     
       10. The twin-clutch type transmission unit according to  claim 8 , wherein each of the first input shaft and the second input shaft comprise an inner-outer double shaft having an inner input shaft and an outer input shaft, and the clutch synchronization device for synchronizing the rotation of the first input shaft and the rotation of the second input shaft is provided between the inner input shaft and an end portion of the outer input shaft. 
     
     
       11. The twin-clutch type transmission unit according to  claim 7 , wherein said clutch synchronization device comprises one of said drive gears formed on the first input shaft having a hole formed therein, and a projection formed on one of adjacent said drive gears formed on the second input shaft; and wherein said hole is operable to engage with said projection. 
     
     
       12. The twin-clutch type transmission unit according to  claim 7 , wherein said clutch synchronization device is arranged between the first input shaft and an end portion of the second input shaft. 
     
     
       13. A motorcycle comprising
 an engine having a crankshaft; and 
 a twin-clutch type transmission unit operatively connected with said crankshaft; 
 said twin-clutch type transmission unit comprising 
 a set of clutches comprising a first clutch and a second clutch; 
 a first input shaft and a second input shaft provided respectively with said clutches for transmission and interruption of input from the crankshaft; 
 a plurality of drive gears provided on the first and second input shafts; 
 an output shaft provided with a plurality of driven gears operable to mesh with drive gears, with the clutches of the first input shaft and the second input shaft being alternately disengaged and engaged so as to perform a gear shift; and 
 a clutch synchronization device for synchronizing rotation of the first input shaft and rotation of the second input shaft, the clutch synchronization device comprising a first drive gear being rotationally fixed on the first input shaft and a second drive gear being rotationally fixed on the second input shaft, said clutch synchronization device being operative to directly connect the first input shaft and the second input shaft; 
 wherein at a time of vehicle starting: 
 the first input shaft and the second input shaft are connected to each other through the clutch synchronization device; 
 the clutches of both the first and second input shafts are simultaneously engaged; such that motive force from the prime mover is transmitted by the first clutch to the first input shaft and simultaneously by the second clutch to the second input shaft, 
 the motive force transmitted to the second input shaft by the second clutch is further transmitted from the second input shaft to the first input shaft by the clutch synchronization device, 
 a sum of the motive force transmitted from the first clutch to the first input shaft and the motive force transmitted from the clutch synchronization device to the first input shaft is transmitted from the first input shaft to the output shaft, 
 and a loading of the first and second clutches is shared during the time of vehicle starting. 
 
     
     
       14. A motorcycle according to  claim 13 , wherein after the vehicle starting, the first input shaft and the second input shaft are disconnected from each other at a time when rotation of the crankshaft reaches a predetermined rotating speed. 
     
     
       15. A motorcycle according to  claim 13 , wherein said clutch synchronization device is arranged between the first input shaft and an end portion of the second input shaft. 
     
     
       16. A motorcycle according to  claim 13 , wherein said clutch synchronization device comprises one of said drive gears formed on the first input shaft having a hole formed therein, and a projection formed on one of adjacent said drive gears formed on the second input shaft; and wherein said hole is operable to engage with said projection. 
     
     
       17. A motorcycle according to  claim 13 , wherein the first input shaft and the second input shaft comprise an inner-outer double shaft having an inner input shaft and an outer input shaft; and
 said clutch synchronization device for synchronizing the rotation of the first input shaft and the rotation of the second input shaft is arranged between the inner input shaft and an end portion of the outer input shaft. 
 
     
     
       18. A motorcycle according to  claim 14 , wherein the first input shaft and the second input shaft comprise an inner-outer double shaft having an inner input shaft and an outer input shaft; and
 said clutch synchronization device for synchronizing the rotation of the first input shaft and the rotation of the second input shaft is arranged between the inner input shaft and an end portion of the outer input shaft. 
 
     
     
       19. A motorcycle according to  claim 17 , wherein said set of clutches is arranged at an end portion of the first and second input shafts; and wherein a right-side portion of the inner input shaft extending in the left-right direction is inserted in the outer input shaft such that the inner input shaft is rotatably supported on the outer input shaft through a bearing. 
     
     
       20. A motorcycle according to  claim 18 , wherein the clutch synchronization device comprises a dog-type clutch in which at least one of the gears provided at the end portion of the outer input shaft and one of the gears provided on the inner input shaft adjacent to said at least one of the gears provided at the end portion of the outer input shaft is moved in an axial direction to be fitted to the said one the gears provided on the inner input shaft.